Direct laser deposition is an additive layer process used to produce complex and intricate shapes that cannot easily be produced by any other manufacturing method. Direct laser deposition is a powder bed process in which a component is built up layer by layer by the melting and fusion of a plurality of layers of the component material.
A single layer of the component material is deposited onto a base plate and then fused by a high energy laser source. The base plate is then incrementally lowered and another layer of the powder material is applied to the base plate. This process is then repeated layer by layer until the finished component is produced.
The rapid heating and cooling cycles occurring during the fusion process, as the laser source follows the profile of the component, are known to cause residual stresses within the component. These residual stresses may in turn cause deformation of the component geometry.
This deformation can limit the type of materials that can be successfully deposited using the direct laser deposition process. For example, metals and metal alloys that are considered to be weldable, such as nickel superalloys containing high gamma prime volume fractions, are difficult to deposit by the direct laser deposition process due to post build cracking caused by residual stresses.
It is known to provide heating to the powder bed containing the component as it is formed, in order to reduce the thermal gradients that can induce residual stresses and hence the incidence of cracks whether during or after build. However, heating the entire powder bed is energy intensive and hence costly.
Alternatively, local heating may be provided within the powder bed, for example by induction coils. This approach limits the space available within the build chamber and may interfere with the shielding gas flow and the movement of the laser source. Additionally the high frequency current required for induction heating may also interfere with other electrical equipment that forms part of the direct laser deposition.